Engineering Materials – Tutorial Assignment 2, Semester 1 2014
This assignment is based on tutorials and answers should be supported by illustrations (sketches and graphs) wherever relevant. Any references used should be specified after each question.
All Answers must be less than or equal to ¾ of a page in 12 point Font, excluding graphics and references!
This second part of the tutorial assignment is due to be submitted by the end of the lecture in week 12.

7. Explain how you could obtain a minimum yield strength of 900MPa through the full thickness of a 100 mm diameter shaft manufactured from 4340 steel. This explanation should include specific details of the heat treatment processes and include temperatures/time and supporting data and graphs.
NOTE the diameter and steel grade (ie 4340) cannot be altered. (20 marks)

8. How would you differentiate between Surface Corrosion, pitting corrosion and crevice corrosion? (7 marks)

9. Would Iron (Fe) corrode in de-aerated dilute hydrochloric Acid (HCl)? (6 Marks)
Give the Equations and calculate the Gibbs Free Energy to determine your answer.

10. A steel tie rod 23 mm in diameter has the following minimum properties:
Yield Strength = 700MPa
Tensile Strength = 800Mpa
Fracture Toughness = 95MPam0.5

It was subjected to an axial tensile force of 300kN.
Determine its mechanical safety with respect to ductile and brittle fracture. Consider ß = 1.
Hint: Brittle fracture would occur if the rod contained a crack. (10 marks)

11. What would the following features on the fractured surface face of a broken shaft tell you about the mode of failure and the levels of stress that that shaft experienced? (7 marks)

(a) beach marks
(b) ratchet marks
(c) size of final fracture area

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128.

practical 2

PRAC 2 COMPARISON OF TENSILE PROPERTIES
1)    Fill in the table on the report Doc with the data entered in Class and also use data from the     Data Excel File and calculate the estimated Max Force for all materials on page 1.
The best way to do this is to use the data to generate EXCEL PLOTS. I.E. Copy the file, then    delete the material data for the samples that you are not going to use.
Then Insert extra columns and calculate the STRESS and STRAIN from the Force and     EXTENSION data.
Then generate two Excel plots. One for Force/Extension and one for Stress/Strain

2)    For the Report Doc Tabulate the Raw Data for your polymer sample and put that in the top     row, then choose three other test samples to fill in the other three rows for the     Force/Extension table.
3)     Do the same for the Stress/Strain Section.
4)    Complete the rest of the Prac write up and don’t forget to put in references.

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